2520
Several companies send exploratory missions to the Sirius system, one of the first to see serious colonization. The region’s very high metallicity (over 700% that of Sol) spurs a great deal of interest in it and its potential, this despite its lack of stable habitable worlds. What solid worlds that are there are resource-rich, and the asteroid concentration is nearly 50 times that of Sol. This does present navigating problems though since impact risks are high. In the early days of exploration when the orbits where still being plotted, Sirius was seen as an adventurous and high-stakes destination for both entrepreneurs and mega-corps alike.

2560Sirius Ab, a solid world lying too close to the star for humans to really settle it comfortably, still possesses ample sources of water despite millions of years of evaporation from the primary star's solar winds. The planet's eccentric orbit brings it close enough to the star to produce dynamic blow-off of water vapour creating a massive comet-like tail (which granted it the nickname Big Comet). The world is a hot destination for ambitious water-hunting companies and groups, which is a precious commodity in space for many reasons, and receives gradual increases in population because of it.

2600
Much of the resources being extracted and refined in Sirius are sent back to Sol to help continue terraforming and other mega-scale projects, but growth still continues in the young system, and many very large space stations and habitats are established as an alternative to worlds. The largest of these at this time is a 90+ kilometer long hab in orbit of Big Comet known as the Nexus, it is a dual-cylinder structure that supports nearly 20 million inhabitants and redirects energy beams from massive solar collector arrays to dozens of smaller habs throughout the system.

2700
Sirius reaches it's general peak of success, 3 worlds have undergone partial terraforming (through the use of large dome-cities and orbital sunshades), and the number of large habs in the system is more than 100. The system has become known for it's great Forges, giant structures intended to construct space stations, habs, and (eventually) very large ships. Those the later are effectively large mobile space stations more than true ships.

2732
The Sirius System suffers a major catastrophe that damages FTL dynamics within the nearby region of space, for nearly 300 years Sirius remains effectively isolated from the rest of the Terran network.

3000
The Solar Union becomes sufficiently organized and influential to annex several star systems and their constituent colonies. This eventually comes to includes Sirius.

3080
A conflict begins in Sirius that will come to be known as the Orbital Wars, fought between local Sirian loyalists and foreigh mega-corps. The conflict is triggered when a 50 megaton asteroid is diverted by means of thermonuclear warheads to impact an important hab. Though the resulting orbit takes over 6 T-months to reach it's target, the resulting confusion and skirmishes throughout the system prevents the mega-corps from enacting a diversion manoeuvre of their own, and the asteroid strikes. 13 more such attacks are enacted before intervention from the interstellar community (most notably from the SU) ends the conflict.

4500 and later
The SU's area of influence includes nearly all star within 200 Lightyears of it's capital system (Sol).

Trivia

Sirius's solar winds are approximately 20 times stronger than that of Sol, this has led to extensive use of solar sail technology for interplanetary travel throughout the system.

Sirius is home to the renowned Looking Glass, one of the largest single terraforming structures in the Terran Sphere.